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linux/block/Kconfig
Jan Kara ed5cc702d3
block: Add config option to not allow writing to mounted devices 
Writing to mounted devices is dangerous and can lead to filesystem
corruption as well as crashes. Furthermore syzbot comes with more and
more involved examples how to corrupt block device under a mounted
filesystem leading to kernel crashes and reports we can do nothing
about. Add tracking of writers to each block device and a kernel cmdline
argument which controls whether other writeable opens to block devices
open with BLK_OPEN_RESTRICT_WRITES flag are allowed. We will make
filesystems use this flag for used devices.

Note that this effectively only prevents modification of the particular
block device's page cache by other writers. The actual device content
can still be modified by other means - e.g. by issuing direct scsi
commands, by doing writes through devices lower in the storage stack
(e.g. in case loop devices, DM, or MD are involved) etc. But blocking
direct modifications of the block device page cache is enough to give
filesystems a chance to perform data validation when loading data from
the underlying storage and thus prevent kernel crashes.

Syzbot can use this cmdline argument option to avoid uninteresting
crashes. Also users whose userspace setup does not need writing to
mounted block devices can set this option for hardening.

Link: https://lore.kernel.org/all/60788e5d-5c7c-1142-e554-c21d709acfd9@linaro.org
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20231101174325.10596-3-jack@suse.cz
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Christian Brauner <brauner@kernel.org>
2023-11-18 14:59:25 +01:00

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# SPDX-License-Identifier: GPL-2.0
#
# Block layer core configuration
#
menuconfig BLOCK
bool "Enable the block layer" if EXPERT
default y
select FS_IOMAP
select SBITMAP
help
Provide block layer support for the kernel.
Disable this option to remove the block layer support from the
kernel. This may be useful for embedded devices.
If this option is disabled:
- block device files will become unusable
- some filesystems (such as ext3) will become unavailable.
Also, SCSI character devices and USB storage will be disabled since
they make use of various block layer definitions and facilities.
Say Y here unless you know you really don't want to mount disks and
suchlike.
if BLOCK
config BLOCK_LEGACY_AUTOLOAD
bool "Legacy autoloading support"
default y
help
Enable loading modules and creating block device instances based on
accesses through their device special file. This is a historic Linux
feature and makes no sense in a udev world where device files are
created on demand, but scripts that manually create device nodes and
then call losetup might rely on this behavior.
config BLK_RQ_ALLOC_TIME
bool
config BLK_CGROUP_RWSTAT
bool
config BLK_CGROUP_PUNT_BIO
bool
config BLK_DEV_BSG_COMMON
tristate
config BLK_ICQ
bool
config BLK_DEV_BSGLIB
bool "Block layer SG support v4 helper lib"
select BLK_DEV_BSG_COMMON
help
Subsystems will normally enable this if needed. Users will not
normally need to manually enable this.
If unsure, say N.
config BLK_DEV_INTEGRITY
bool "Block layer data integrity support"
help
Some storage devices allow extra information to be
stored/retrieved to help protect the data. The block layer
data integrity option provides hooks which can be used by
filesystems to ensure better data integrity.
Say yes here if you have a storage device that provides the
T10/SCSI Data Integrity Field or the T13/ATA External Path
Protection. If in doubt, say N.
config BLK_DEV_INTEGRITY_T10
tristate
depends on BLK_DEV_INTEGRITY
select CRC_T10DIF
select CRC64_ROCKSOFT
config BLK_DEV_WRITE_MOUNTED
bool "Allow writing to mounted block devices"
default y
help
When a block device is mounted, writing to its buffer cache is very
likely going to cause filesystem corruption. It is also rather easy to
crash the kernel in this way since the filesystem has no practical way
of detecting these writes to buffer cache and verifying its metadata
integrity. However there are some setups that need this capability
like running fsck on read-only mounted root device, modifying some
features on mounted ext4 filesystem, and similar. If you say N, the
kernel will prevent processes from writing to block devices that are
mounted by filesystems which provides some more protection from runaway
privileged processes and generally makes it much harder to crash
filesystem drivers. Note however that this does not prevent
underlying device(s) from being modified by other means, e.g. by
directly submitting SCSI commands or through access to lower layers of
storage stack. If in doubt, say Y. The configuration can be overridden
with the bdev_allow_write_mounted boot option.
config BLK_DEV_ZONED
bool "Zoned block device support"
select MQ_IOSCHED_DEADLINE
help
Block layer zoned block device support. This option enables
support for ZAC/ZBC/ZNS host-managed and host-aware zoned block
devices.
Say yes here if you have a ZAC, ZBC, or ZNS storage device.
config BLK_DEV_THROTTLING
bool "Block layer bio throttling support"
depends on BLK_CGROUP
select BLK_CGROUP_RWSTAT
help
Block layer bio throttling support. It can be used to limit
the IO rate to a device. IO rate policies are per cgroup and
one needs to mount and use blkio cgroup controller for creating
cgroups and specifying per device IO rate policies.
See Documentation/admin-guide/cgroup-v1/blkio-controller.rst for more information.
config BLK_DEV_THROTTLING_LOW
bool "Block throttling .low limit interface support (EXPERIMENTAL)"
depends on BLK_DEV_THROTTLING
help
Add .low limit interface for block throttling. The low limit is a best
effort limit to prioritize cgroups. Depending on the setting, the limit
can be used to protect cgroups in terms of bandwidth/iops and better
utilize disk resource.
Note, this is an experimental interface and could be changed someday.
config BLK_WBT
bool "Enable support for block device writeback throttling"
help
Enabling this option enables the block layer to throttle buffered
background writeback from the VM, making it more smooth and having
less impact on foreground operations. The throttling is done
dynamically on an algorithm loosely based on CoDel, factoring in
the realtime performance of the disk.
config BLK_WBT_MQ
bool "Enable writeback throttling by default"
default y
depends on BLK_WBT
help
Enable writeback throttling by default for request-based block devices.
config BLK_CGROUP_IOLATENCY
bool "Enable support for latency based cgroup IO protection"
depends on BLK_CGROUP
help
Enabling this option enables the .latency interface for IO throttling.
The IO controller will attempt to maintain average IO latencies below
the configured latency target, throttling anybody with a higher latency
target than the victimized group.
Note, this is an experimental interface and could be changed someday.
config BLK_CGROUP_FC_APPID
bool "Enable support to track FC I/O Traffic across cgroup applications"
depends on BLK_CGROUP && NVME_FC
help
Enabling this option enables the support to track FC I/O traffic across
cgroup applications. It enables the Fabric and the storage targets to
identify, monitor, and handle FC traffic based on VM tags by inserting
application specific identification into the FC frame.
config BLK_CGROUP_IOCOST
bool "Enable support for cost model based cgroup IO controller"
depends on BLK_CGROUP
select BLK_RQ_ALLOC_TIME
help
Enabling this option enables the .weight interface for cost
model based proportional IO control. The IO controller
distributes IO capacity between different groups based on
their share of the overall weight distribution.
config BLK_CGROUP_IOPRIO
bool "Cgroup I/O controller for assigning an I/O priority class"
depends on BLK_CGROUP
help
Enable the .prio interface for assigning an I/O priority class to
requests. The I/O priority class affects the order in which an I/O
scheduler and block devices process requests. Only some I/O schedulers
and some block devices support I/O priorities.
config BLK_DEBUG_FS
bool "Block layer debugging information in debugfs"
default y
depends on DEBUG_FS
help
Include block layer debugging information in debugfs. This information
is mostly useful for kernel developers, but it doesn't incur any cost
at runtime.
Unless you are building a kernel for a tiny system, you should
say Y here.
config BLK_DEBUG_FS_ZONED
bool
default BLK_DEBUG_FS && BLK_DEV_ZONED
config BLK_SED_OPAL
bool "Logic for interfacing with Opal enabled SEDs"
depends on KEYS
select PSERIES_PLPKS if PPC_PSERIES
select PSERIES_PLPKS_SED if PPC_PSERIES
help
Builds Logic for interfacing with Opal enabled controllers.
Enabling this option enables users to setup/unlock/lock
Locking ranges for SED devices using the Opal protocol.
config BLK_INLINE_ENCRYPTION
bool "Enable inline encryption support in block layer"
help
Build the blk-crypto subsystem. Enabling this lets the
block layer handle encryption, so users can take
advantage of inline encryption hardware if present.
config BLK_INLINE_ENCRYPTION_FALLBACK
bool "Enable crypto API fallback for blk-crypto"
depends on BLK_INLINE_ENCRYPTION
select CRYPTO
select CRYPTO_SKCIPHER
help
Enabling this lets the block layer handle inline encryption
by falling back to the kernel crypto API when inline
encryption hardware is not present.
source "block/partitions/Kconfig"
config BLK_MQ_PCI
def_bool PCI
config BLK_MQ_VIRTIO
bool
depends on VIRTIO
default y
config BLK_PM
def_bool PM
# do not use in new code
config BLOCK_HOLDER_DEPRECATED
bool
config BLK_MQ_STACKING
bool
source "block/Kconfig.iosched"
endif # BLOCK
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